Various polymers have been used to prepare tire treads and to improve the properties and performance of the treads. High performance tires for general as well as special purposes generally are characterized as having improved traction, improved handling, lower wear and higher heat resistance than standard passenger tires. Accordingly, high performance tires will include treads made from compounds which generally have the following properties: high hysteresis loss, high tensile strength, low durometer, low viscosity, high thermal resistance, skid resistance, etc. High performance tires are useful in automobiles and motorcycles for highway or track use.
The polymerization of conjugated dienes such as 1,3-conjugated dienes to form elastomeric homopolymers and copolymers utilizing various initiator systems is known. For example, such polymerizations can be initiated with organometallic compounds wherein the metal is a Group I metal such as lithium. These polymers and copolymers of conjugated dienes are useful for tire rubbers, molded rubber goods, molding compounds, surface coatings, etc.
Various organometallic compounds have been described in the literature as useful in the polymerization and copolymerization of conjugated dienes. Among the catalysts which have been proposed are various alkali metal acetylides. For example, U.S. Pat. No. 3,303,225 describes the use of metalated 1-acetylenes as active catalysts in the polymerization of vinylidene-containing monomers. Alkali metal acetylides containing one or more metal atoms are prepared by reacting an organo alkali metal compound with an acetylene under conditions to effect step-wise replacement of, first, the acetylenic hydrogen atom, and, second, the hydrogen atoms attached to the carbon atom which is alpha to the acetylenic linkage.
U.S. Pat. No. 4,677,165 describes rubber compositions useful particularly for tire treads which comprise: a styrene-butadiene copolymer rubber prepared by random copolymerization of styrene with 1,3-butadiene by solution polymerization techniques utilizing an organic lithium compound as catalyst; from 80 to 250 phr of carbon black having a surface area of 100 to 400 m.sup.2 /g; and 30 to 280 phr of an aromatic oil. It is essential that the styrene-butadiene copolymer satisfies six requirements as identified in the specification and claims including the presence of one or more specific groups introduced into a molecular terminal or chain of the copolymer.
U.S. Pat. No. 2,964,083 describes curable rubber tire tread stock and pneumatic tires having a tread portion made of such stock. The tread stock comprises a copolymer containing a major amount of a conjugated diolefinic compound and a minor amount of a copolymerizable monoolefinic compound such as styrene, a fine reinforcing high abrasion carbon black and at least 30 parts by weight of a compatible soft oil per 100 parts by weight of the copolymer.
Styrene-butadiene elastomers comprising blends of different styrene-butadiene copolymers are described as being useful for treads of high performance tires in U.S. Pat. No. 4,866,131. The elastomers can be extended with oil to increase the hysteresis loss value. Aromatic oils having a viscosity gravity constant according to ASTM D-2501 in the range of 0.900 to 1.100 are described as suitable. The use of a low temperature plasticizer ester and/or a naphthenic or paraffinic softener to improve the properties of carbon black filled styrene-butadiene rubbers is described in U.S. Pat. No. 4,748,199.
U.S. Pat. No. 4,791,178 describes rubber compositions for use in tires which comprise certain mixtures of copolymers of a conjugated diene and monovinyl aromatic hydrocarbons. To obtain high hysteresis loss, the patentees suggest that an extender oil be blended into rubber compositions in amounts of from 30-200 parts by weight based on 100 parts by weight of the rubber component. Amounts of from 50 to 200 parts of oil are preferred. The use of 60 to 200 parts by weight of carbon black having an average particle size of not more that 300 .ANG. also is disclosed as producing rubber composition with high hysteresis loss.